Manufacture of grid resistances



L. SATCHWELL.

MANUFACTURE OF emu RESISTANCES..

APPLICATION FILED 0C T.18,1920

I PatentedJune 6, 1922.

4 SHEETS-SHEET 1- L. 'SATCHWELL.

MANUFACTURE OF GRID RESISTANCES. APPLICATION FILED OCT, 13 L920.

1,418,834. awmedme 6, 1922.

4 SHEETS-SHEET 2.

l Jrzsulahion m F1655. F /a: .5.

flwmvw.

PER 45/4 L. SATCHWELL.

MANUFACTURE 0? GR) RESASTANCES.

APPLICATION FILED OCT. 18 1920.

1,418,834. ,Patenwuune 6,1922.

4 SHEETS-SHEET 3.

l 'lill w I a i g M IV: I M h l i w? I at r 4 n 1 I a g k ,6 i

' 1 i i Um LL a l??? L l i -21 22 l QQQ l H5: 8. l2 U VEI ITOR,

PEP

Brion/wry.

L. SATCHWELL. MANUFACTURE OF GRID RESISTANCES.

APPLICATION FILED OCT. 18, 1920.

Patented Jane 6, 1922.

E 0 MW. e

mgpm

UNITED STATES PATENT OFFICE.

MANUFACTURE OF GRID RESISTANCES.

Specification of Letters Patent.

Patented June 6, 1922.

Application filed October 18, 1920. Serial No. 417,747.

To (ZZZ whom it may concern Be it known that I, LEONARD SA'roHwnLL, a subject of the King of Great Britain and Ireland, residing at 70 Ardwyn, Garden Suburb, Burry Port, Caermarthen,

ful Improvements in the Manufacture of Grid Resistances, of which the following is a specification.

This invention relates to electrical resistances and in particular to grid resistances, that is to say, resistances in which the current path is bent upon itself in a series of parallel and closely adjacent lengths, so as to be substantially free from self-induction. The purpose of the invention is to produce a resistance of this kind which can be manufactured cheapl and shall be robust and reliable. A furt er purpose of the invention is to produce a stamped sheet metal resistance which shall be rigidly supported throughout substantially its whole length by the aid of insulating separators interposed between adjacent parallel parts of the strip, while yet the greater part of the surface of the current-carrying metal shall be surrounded by, and freely exposed to, the air, so as readily to radiate the heat generated within it. I

To these ends one embodiment of the invention comprises a succession of lengths of stamped strip between which are inserted insulating separators of much less width than the strips, the lengths of strip and the separators being clamped into a rigid whole. In a fuller development of the invention the stamped strips so assembled and clamped with separators are perforatedalong their length opposite the separators, so that the portion of the metal gripped between the separators is substantially eliminated from the current path.

The invention also includes a resistance formed of a continuous stamped strip having notches in its edge at intervals, which is bent upon itself at the notches and assembled with separators of much less width than the strip interposed between the parallel lengths thus formed, so that there are spaces between the edges of the strips in line with the notches; if a resistance thus constructed is set with the strips vertical vigorous convection currents are set up between the edges of the strips and through the notches which effectively cool the strip. It is preferred to form the separators of South \Vales, England, have invented new and usestamped sheet metal having its surface covered with insulation. Two, three or more of such stamped and insulated strips are 1nterposed between each pair of successive lengths of the resistant strip. By suitable variation of the thickness of the separators a resistance may be thus constructed for any of awide range of time ratings.

Constructions according to the invention are illustrated in the accompanying draw- 1n 's- Figure 1 being an elevation, and

Figure 2 a sectional plan of one section of a rheostat constructed according to this inventlon.

Figures and 4 are details of the resistant strip and insulating separator respectively.

Figure 5 illustrates a modified construction of strip.

Figures 6, 7 and 8, and 9 are alternative forms of grid.

The resistant element consists of thin stamped sheet metal strips, as shown in Fig. ure 3. Preferably the strip is continuous throughout a grid, or even over a succession of grids. A central slot 1 is cut in each length of the strip, which is of slightly less width than the separator shown in Figure 4:. This separator may consist of a strip of metal insulated over all its surface, or it mav be of insulating material suited to withstand the heat and pressure to which it will be subjected. If a metal separator is to be made by stamping the material stamped must be thin; and a separator will generally need to consist of three or four stampings insulated from the resistant strip by asbestos paper oi the like. The resistant strip has transverse slots cut in it at the end of each length, as seen at 2. The strip is bent backwards and forwards upon itself where the transverse slots 2 occur, and neighboring lengths lie in such close proximity one to the other that the rheostat has little inductance. Theyhave only to be spaced apart by the separators sufficiently to avoid any danger of neighboring lengths coming into contact as the result of deformation of their edges when hot. The folded strip, as seen at 3 in Figures 1 and 2. is threaded upon bolts which are passed through end plates 4. Between each two lengths of the resistant strip is insertedan insulating strip 5, such as is shown in Figure 4. The bolts are suitably insulated from the resistant strip, for instance by a mica sleeve. Nuts 6 placed on them outside the end plates 1. with spring washers T interposed. serve to compress the several lengths of strip and insulating separators into a rigid block forming one section of a rheostat.

Prefe ably copper strips 8. of similar section to the separators 5 but of greater length. are interposed between the end lengths of the resistant element and the end plates .4.

very small width of the metal of the stamping. Practically the whole surface of the current carrying metal is exposed to the air. so that heat is freely radiated. Moreover. the slots 2 enable the heated air rising between the strips to pass freely away at the top while fresh air enters beneath. lt will be found that a resistant strip of given dimensions may be used in the manufaqture of resistances for a wide range of conditions; for a slight increase in the space between successive lengths of the strip will materially increase the time rating of the resistance.

By a slight modification of the stamping, as indicated in Figure 5. it is possible to arrange that the stamping is rigidly gripped between its two neighboring separatois, while the metal between the separators is practically eliminated from the current path. It will be obvious that many modifications in the form of the openings cut in the strip made be made consistently with observance of this condition. It is notessential that the separators should be in the middle of the strips. though this arrangement gives the.

mechanical strength is of less importance.

This increases the 'adiating power and tends to the production of a compact and emcient resistant unit.

Figure 6 shows a slight modification of this construction. the grid being made of a large number of short separate stampings 10,'each having a central opening. substantially in the fashion shown in Figures. 3 and 4. These stampings are threaded upon bolts 11 having insulating sleeves 12. and between each pair of resistant strips there is threaded on the bolts an insulating separator 13. These separators are shorter than the resistant strips and are located alternately towards the one and the other end of the strips. For instance, the insulating strip 13 appearing in Figure 6 is threaded only on the centre and lower bolts 11. Upon the upper bolt there is threaded instead a conducting washer 14: which serves to make connection at this end between the strip 10 shown and the next stripv The next separator 13 will be threaded upon the centre and upper bolts 11 and there will be a conducting washer ll threaded on the lower bolt. these washers being of the same thickness as the separators. In other respects the resistant strips may be built up in substantially the fashion shown. in Figures 1 and 2.

Figures 7 and b show a stamped resistance grid of substantially known type. but assembled in the manner which constitutes the subject of this application. The resistant strip itself is 15. A succession of strips is built up upon steel draw plates 16 which are surrounded by mica or other insulation 17. Between the successive lengths of the resistant element there are threaded upon the plates 16. loops or substantially U-shaped washers of insulation 18, which represent the separators 5 of Figures 1 and 2. This stamping also may be made continuous as is shown in the drawing and bent backwards and forwards upon itself at 22. At the end of the strip 16 are studs for tightening up the unit when assembled. or. alternatively. the assembled unit may be compressed and taper steel pins 19 driven through slots 20 in the draw plates 16 on the outside of the end plates 21.

It will be understood that conducting strips such as 8 may be inserted at any desired points in a rheostat for the purpose of making external connections.

Vhere a resistance is required for very small currents a slight modification may be desirable. It is not con 'cnient to reduce the thickness of the resistant strip below a certain minimum; otherwise its mechanical strength is too n'iuch reduced and the tendency to cockle upon heating is increased. For such cases slots may be cut in a resistant strip alternately from opposite sides as shown at 23 in Figure 9, which shows a portion ofastrip before it is bent upon itself. and its perforations 2% threaded upon bolts in the manner described in connection with Figure 6. These slots need only be very narrow. sutlicient to allow for the eX pansion of the short length of metal between them. and they materially increase the length of the current path by making it zigzag from side to side of the strip. The strip is bent along the lines 25-20, so that the notches 2G permit the passage of a convection current of air as in the constructions already described.

What I claim is:

1. An electrical resistance comprising a stamped strip of metal having notches at intervals along its edge. said strip being bent succession of parallel strips in electrical con, nection, said strips being perforated along: the greater part of their length, separators of slightly greater width than said perfora-l;

means clamping said resistant metal and separators together.

A stamped grid resistance compr sing a succession of parallel strips. forming a zigzag current path, separators interposed between successive strips and :insulating them from one another, said separators con-.

tacting with and supporting said strips throughout their whole length but cover ng less than a thirdof their width, and means clamping said strips gether- I 4. An electrical resistance comprising,

f and separators tions interposed between said strips, Lso-as to support andinsulate them from onefan; other throughout their length but to cover little of the conducting path, andgmeans clamping said strips andseparatorsitof gather.

5. An electrical resi mhe edh prisinga flat resistant stripbentfupojn itself, witl i' narrower insulating separators interposed ing'perforations opposite the sep-aratorsof as substantially to removefrom the current path the portions of the strip covered by said separators.

6. An electrical resistance comprising a succession of stamped strips in electrical connection, in combination with insulated bolts upon which said strips are threaded by their perforations, insulating separators of less width, than said strips interposed between said strips and also threaded on said bolts,

and nuts upon said bolts clamping said strips and separators together.

7. An electrical resistance comprising a stamped strip of metal having notches at intervals along its edge, said strip being bent parallel to itself at said notches, separators of muchless width than said strip located between adjacent lengths of strip so as to leave spaces between the edges of adjacent lengths in line with said notches, and means clamping said strip and separators together.

8. An electrical resistance comprising a stamped strip of metal having notches at intervals along its edge and having perforations along its length not in line with said notches, said strip being bent parallel to itself at said'notohes, separators of much less :width than said strip located between adjacent lengths of strip covering said perforations and leaving spaces between the edges of adjacent lengths in line with said notches,

and means clamping said strip and'separators together.

9.]An electrical resistance comprising a stamped strip of metal having notches at (intervalsalong. its edge and having perforaztionsl along its length not in line with said notches, in combination with bolts upon which successive'lengths of said strip bent threaded by means-of their perforations,

located between adjacent lengthsof strip-so as to leave spaces between, the'edges of said [parallel to "each other at said notches are stripf inline with said notches, and nuts I "upon said bolts clamping said stripand sepa H ,rators togethe between its parallel porti'ons,sa1d stri h y.

d itricallyf [continuous succession ,1 of parallel .substantially'the width of the separators so' LEONARD SATCHWELL.

10;A'gridfresistance, comprising an elec-' 

